Highly-depleted laser doped semiconductor volume

ABSTRACT

A device with increased photo-sensitivity using laser treated semiconductor as detection material is disclosed. In some embodiments, the laser treated semiconductor may be placed between and an n-type and a p-type contact or two Schottky metals. The field within the p-n junction or the Schottky metal junction may aid in depleting the laser treated semiconductor section and may be capable of separating electron hole pairs. Multiple device configurations are presented, including lateral and vertical configurations.

I. TECHNICAL FIELD

The present disclosure relates to systems and methods for configuring anenhanced photodiode with increased photosensitivity. In particular, thedisclosure relates to an enhanced photodiode using laser treatedsemiconductor as detection material that separates electron hole pairsusing an electric field generated by a variety of sources, including p-njunctions and Schottky junctions.

II. BACKGROUND

The design of a sensitive photodetective element involves considerationof photon absorption, exciton or electron hole pair (EHP) generation andEHP separation. For example, the materials in a silicon p-n junction ora Schottky metal junction are generally good absorbers of visible lightradiation. That is, devices incorporating p-n junctions or Schottkymetal junctions provide high rates of photon absorption. With theabsorption of each photon, there is a probability that the absorbedphoton will generate an EHP. If the EHP is generated in the depletionregion of the junction, the applied or built in electric field willcause the EHP constituents to drift in opposite directions due to theopposing electric charge signs. If the EHP is not separated by anelectric field, the probability is increased that the electron and holewill recombine and reduce the photodetective efficiency of the device.

III. SUMMARY

The doping of silicon using an ultrafast femtosecond laser has beenshown to impart effective photon absorption capabilities, extend theabsorption spectral cutoff, and decrease the optical absorptioncoefficient. Doping during laser ablation and rapid cooling may causeself forming nanocrystals comprising a combination of dopant, substrate,and impurities that allow these characteristics of laser-dopedsemiconductors. The high concentration of localized nanocrystals canform quantum confinement in the form of quantum wells or quantum dots.In these cases, the confinement of charges is discretized to certainenergy levels within the bandgap of the substrate. If the concentrationand distribution of these quantum structures is optimized, anintermediate band is formed within the bandgap and a plurality of Fermilevels (e.g., three) are defined. Structures of these types can decreasethe optical absorption coefficient and extend the optical cutoffwavelength of a photodetector. A device designed to optimize theefficient collection of EHPs in such a structure may provide an electricfield to separate the positive and negative charge carriers within thedevice. Therefore, an applied field across the photodetective volumepromotes an efficient photodetector.

One or more embodiments provide a photodiode including an n-typesection, a p-type section, and a laser treated semiconductor section.The laser treated semiconductor section may be disposed between then-type section and the p-type section such that the n-type section andthe p-type section can generate an electric field substantially capableof depleting at least a portion of the laser treated semiconductorsection of free carriers and separating resulting electron-hole pairsgenerated in the laser treated semiconductor section. The laser treatedsemiconductor section may comprise a net doped n-type material and then-type section may have a higher level of n-doping than the lasertreated semiconductor section. Alternatively, the laser treatedsemiconductor section may comprise a net doped p-type material and thep-type section may have a higher level of p-doping than the lasertreated semiconductor section. The photodiode may further comprise apair of electrical contact points, one on either side of the lasertreated semiconductor section. The photodiode may further comprise asubstrate proximal to the laser treated semiconductor section and atleast a pair of electrical contact points, one proximal to a face of thelaser treated semiconductor section and the other proximal to a face ofthe substrate opposing the face of the laser treated semiconductorsection. The photodiode may also comprise a substrate proximal to thelaser treated semiconductor section and a plurality of electricalcontact points disposed proximal to a face of the laser-treatedsemiconductor section. In some embodiments, the n-type section maypartially enclose the p-type section and the laser treated semiconductorsection. Alternatively, the p-type section may partially enclose then-type section and the laser treated semiconductor section.

One or more embodiments provide a photodiode including a first Schottkycontact, a second Schottky contact, and a laser treated semiconductorsection. The laser treated semiconductor may be at least partiallydisposed between the first Schottky contact and the second Schottkycontact. The first Schottky contact may have a higher work function thanthe second Schottky contact, such that the first Schottky contact andthe second Schottky contact generate an electric field capable ofsubstantially preventing electron-hole pairs generated by the lasertreated semiconductor section from recombining in at least some portionof the laser treated semiconductor section. The Schottky contacts maycomprise a pair of electrical contact points, one on either side of thelaser treated semiconductor section. The photodiode may further comprisea substrate proximal to the laser treated semiconductor section and theSchottky contacts comprising at least a pair of electrical contactpoints, one proximal to a face of the laser treated semiconductorsection and the other proximal to a face of the substrate opposing theface of the laser treated semiconductor section. The photodiode mayfurther comprise a substrate proximal to the laser treated semiconductorsection and the Schottky contacts providing a plurality of electricalcontact points disposed proximal to a face of the laser-treatedsemiconductor section. The first Schottky contact may partially enclosethe second Schottky contact and the laser treated semiconductor section.Alternatively, the second Schottky contact may partially enclose thefirst Schottky contact and the laser treated semiconductor section.

One or more embodiments provide a photodiode including a first dopedsection, a second doped section, and a laser treated semiconductorsection. The second doped section may be substantially bounded by thefirst doped section and the laser treated semiconductor section may besubstantially bounded by the second doped section. The photodiode mayfurther comprise a first and a second contact. The first contact may becoupled to the first doped section and the second contact may be coupledto the second doped section. The first doped section and the seconddoped section may be substantially annular and the laser treated sectionmay be substantially disk shaped. The first doped section may be n dopedand the second doped section may be p doped. Alternatively, the firstdoped section may be p doped and the second doped section may be ndoped.

One or more embodiments provide a photodiode including a first dopedsection comprising at least one subsection, a second doped sectioncomprising at least one subsection, a laser treated semiconductorsection, and a substrate comprising a first side. The laser treatedsemiconductor section, first doped section and second doped section maybe disposed on the first side of the substrate. The second doped sectionmay be substantially bounded by the first doped section and the lasertreated semiconductor section may be substantially bounded by the seconddoped section. The second doped section may comprise a first and asecond subsection. The second doped section first and second subsectionsmay be disposed on either side of the laser treated semiconductorsection. The first doped section may comprise a first and a secondsubsection. The first doped section first and second subsections may bedisposed on the opposite side of the second doped section first andsecond subsections from the laser treated semiconductor section.

One or more embodiments provide a photodiode including a first dopedsection comprising at least one subsection, a second doped sectioncomprising at least one subsection, a laser treated semiconductorsection, and a substrate comprising a first and second side. The lasertreated semiconductor section and the first doped section may bedisposed on the first side of the substrate. The second doped sectionmay be disposed on the second side of the substrate. The laser treatedsemiconductor section may be substantially bounded by the first dopedsection. The first doped section may comprise a first and a secondsubsection being disposed on either side of the laser treatedsemiconductor section.

Other uses for the methods and apparatus given herein can be developedby those skilled in the art upon comprehending the present disclosure

IV. BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, reference is made to the following detailed description ofpreferred embodiments and in connection with the accompanying drawings,in which:

FIG. 1 illustrates an exemplary embodiment of a laser treatedsemiconductor diode where the laser treated semiconductor section islocated between a p-n junction;

FIG. 2 models a laser treated semiconductor section that is reversebiased in energy space to illustrate quantum confinement of a chargespecies within quantum wells and the free drift of the other species inthe depleted material;

FIG. 3 illustrates an exemplary embodiment of a laser treatedsemiconductor diode where the laser treated semiconductor section islocated between Schottky metal contacts;

FIG. 4 models a laser treated semiconductor section under bias in energyspace to illustrate quantum confinement of a charge species withinquantum wells and the free drift of the other species in the depletedmaterial;

FIG. 5 illustrates an exemplary embodiment of a laser treatedsemiconductor diode using a lateral diode configuration;

FIG. 6 illustrates an exemplary embodiment of a laser treatedsemiconductor diode using a vertical diode configuration; and

FIG. 7 illustrates another exemplary embodiment of a lateral diodeconfiguration.

V. DETAILED DESCRIPTION

Some or all embodiments hereof include a photodetection or photovoltaicdevice sensitive to certain electromagnetic wavelengths and formed on asemiconductor substrate. In some embodiments, the device includes aportion comprising a semiconductor material, for example silicon, whichis irradiated by a short pulse laser to create modified micro-structuredsurface morphology. The laser processing can be the same or similar tothat described in U.S. Pat. No. 7,057,256 to Carey et al., which ishereby incorporated by reference. The laser-processed semiconductor ismade to have advantageous light-absorbing properties. In some cases thistype of material has been called “black silicon” due to its visuallydarkened appearance after the laser processing and because of itsenhanced absorption of light and IR radiation compared to other forms ofsilicon, however, the present description is not limited and comprehendsother laser-treated semiconductor materials and resulting properties.

Generally, the wavelength of the irradiating laser pulse for makingblack silicon, its fluence, and pulse width can affect the morphology ofthe microstructured surface. In some embodiments, the laser fluence maybe between about 1.5 kJ/m² and 12 kJ/m², but can vary depending on thesubstrate composition. The choice of the fluence of laser pulsesirradiating a silicon wafer to generate a microstructured layer thereincan also affect the gettering performance (capacity and/or specificity)of a microstructured substrate. In some embodiments hereof, the laserpulse fluence is selected to be greater than about 3 kJ/m². Morepreferably, the fluence may be chosen to be in a range of about 3 kJ/m²to about 10 kJ/m², or a range of about 3 kJ/m² to about 8 kJ/m².

Additionally, the laser pulse length can affect the morphology andabsorption properties of the treated silicon. Irradiation of a substrateas described herein can be done with femtosecond laser pulses orpicosecond or nanosecond pulses. Other factors that can affectmicrostructures morphology include laser polarization and laserpropagation direction relative to the irradiated surface.

In some embodiments, the laser microstructuring of a substrate isperformed in the presence of a mixture of two or more substances toaccomplish the present purposes. For example, silicon samples treated inthe presence of a mixture of SF₆ and Cl₂ exhibit an increase in themicrostructure density at higher partial pressure of SF₆.

We now turn to a description of an exemplary apparatus for detectingelectromagnetic radiation in at least a range of wavelengths of theelectromagnetic spectrum and/or for generating current or voltagethrough the absorption of photons.

FIG. 1 illustrates an exemplary embodiment of a laser treatedsemiconductor diode 100 where the laser treated semiconductor section102 is disposed between a p-section 104 and an n-section 106. The lasertreated semiconductor section 102 absorbs photons from the illumination108 and generates EHPs within the laser treated semiconductor section102. The p-section 104 and the n-section 106 generate an electric fieldthat aids in depleting the laser treated semiconductor section 102 offree charge carriers and separating EHPs generated in the laser treatedsemiconductor section 102. Also, the laser treated semiconductorincludes a plurality of quantum wells 114 that can trap electrons orholes, depending on the type of laser treatment used, creatingadditional free carriers. In an embodiment where the laser treatedsemiconductor section 102 is net n-type, the n-section 106 may be moren-type doped than the laser treated semiconductor section 102. Likewise,in an embodiment where the laser treated semiconductor section 102 isnet p-type, the p-section 104 may be more p-type doped than the lasertreated semiconductor section 102. The exemplary embodiment in FIG. 1provides for a substantially uniform electric field and quantumconfinement of the electrons. In the example shown, the two junctions(n+ type 106 to laser treated semiconductor 102 junction 116 and lasertreated semiconductor 102 to p type 104 junction 118) are both reversebiased and the depletion section from each depletion section extendsinto both sides of each junction.

FIG. 2 models a laser treated semiconductor section in energy space toillustrate quantum confinement of a charge species (either electrons orholes) within quantum wells 214 and the free drift of the other speciesin the depleted material. In this example, electrons 210 are trapped inquantum wells 214 coupled to the conduction band, allowing the holes 212to freely drift. If desired, holes 212 may also be used as the trapspecies by changing the material used, in which case the electrons mayfreely drift. By trapping one species, enhanced photosensitivity isgained by the transport of many carriers of the freely drifting type. Adashed line is used to illustrate the Fermi energy

FIG. 3 illustrates an exemplary embodiment of a laser treatedsemiconductor diode 300 where the laser treated semiconductor section302 is located between a first 304 and second 306 Schottky contact. Thelaser treated semiconductor section 302 absorbs photons from theillumination 308 and generates electron-hole pairs within the lasertreated semiconductor section 302. The first Schottky contact 304 andthe second Schottky contact 306 may be engineered to create an energyband structure that generates an electric field. The first Schottkycontact 304 and the second Schottky contact 306 may be connected to thelaser treated semiconductor section 302 to create metal semiconductorjunctions 310 and 312. The electric field generated by the energy bandstructure separates the EHPs and prevents or reduces the likelihood ofthem recombining. In an exemplary embodiment the work function of thefirst Schottky contact 304 (φ_(m1)) is higher than the work function ofthe second Schottky contact 306 (φ_(m2)). The exemplary embodiment inFIG. 3 also provides for a uniform electric field and quantumconfinement of the electrons.

FIG. 4 models a laser treated semiconductor section under bias in energyspace to illustrate quantum confinement of a charge species (eitherelectrons or holes) within quantum wells 414 and the free drift of theother species in the depleted material. Similar to the charge flow inFIG. 2, metal semiconductor contacts can provide charge and an electricfield across the laser doped material. In a metal semiconductorjunction, majority carriers are injected into the semiconductor. Byusing a laser doped material with minority carrier trapping in aphotodetector, a highly sensitive device may be obtained. In thisexample, the electrons 210 are trapped in the quantum wells 214,allowing the holes 212 to freely drift. A dashed line is used toillustrate the Fermi energy

FIG. 5 illustrates an exemplary embodiment of a laser treatedsemiconductor diode 500 using a lateral diode configuration. A lateraldiode has all of its connections on a single side of the device. Onebenefit to using a lateral configuration is its compatibility with thestandard CMOS process flow. In one exemplary embodiment, the n-type 504and p-type 506 layers are arranged in a substantially annular fashionaround a substantially disk shaped laser treated semiconductor section502. The n-type 504 layer may be connected to a contact 510.Alternatively, depending on the application, the laser treatedsemiconductor section 502 may be connected to a contact 510. The p-typelayer 506 may be connected to the contact 508. In the pictured exemplaryembodiment, the n-type layer 504 is connected to a contact 510 and thep-type layer 506 is connected to a contact 508 at or near the edge ofthe laser treated semiconductor section 502. The p-type layer 506substantially bounds the n-type layer 504. Additionally, the n-typelayer 504 substantially bounds the laser treated semiconductor section502. The laser treated semiconductor used in the laser treatedsemiconductor section 502 provides a decreased optical absorptioncoefficient due to a combined effect from the increased optical pathlength from the nanocrystalline nature of the surface layer and theimpurity state absorption of below band gap wavelengths. The decreasedoptical absorption coefficient allows a shallow junction device 500 toefficiently collect EHPs. In this embodiment, the electric fieldgenerated by the device extends laterally around the device, rather thaninto the depth of the laser treated semiconductor section 502. Thelateral field provides a lower overall leakage current due to fewer bulklevel defects within the substrate.

FIG. 6 illustrates an exemplary embodiment of a laser treatedsemiconductor diode 600 using a vertical diode configuration. A verticaldiode configuration has contacts (606 and 608) on both sides of thedevice. Potential benefits of the vertical diode configuration include:increased fill factor on the detection surface, stronger electricalfields between contacts resulting in increased EHP separation, greaterabsorption depth resulting in increased absorption efficiency. In oneexemplary embodiment, a laser treated semiconductor section 602 may bedisposed on a surface of a substrate 604 along with a p-doped section.The p-doped section may comprise at least one subsection (e.g., p-typecontacts 606). The laser treated semiconductor section 602 may bedisposed between the p-type contacts 606. The substrate may be n-typedoped and may include n-type contacts 608 on the opposite side of thesubstrate 604 from the laser treated semiconductor layer 602.

FIG. 7 illustrates another exemplary embodiment of a lateral diodeconfiguration. In this embodiment, a laser treated semiconductor section702 is disposed on the surface of a substrate 704 along with a p-dopedsection and an n-doped section. The p-doped section may comprise atleast one subsection (e.g., p-type contacts 706). The n-doped sectionmay comprise at least one subsection (e.g., n-type contacts 710). Thelaser treated semiconductor section 602 may be disposed between thep-type contacts 706. The substrate 704 may be n-type doped and includen-type contacts 710 on the same side of the substrate 704 as the lasertreated semiconductor section 702. The laser treated section 702 may besubstantially bounded by the p-type contacts 706. The p-type contacts706 may be substantially bounded by the n-type contacts 710. Byarranging the lateral diode configuration 700 such that the n-typecontacts 710 and the p-type contacts 706 are in close proximity, then-type 710 and p-type 706 layers will have a higher built in voltagethan the n-type 710 to laser treated semiconductor 702 and p-type 706 tolaser treated semiconductor 702 junctions. The high built-in voltagebetween the n-type 710 and p-type 706 layers allows the p-type 706 tolaser treated semiconductor 702 to n-type 710 conduction path todominate. The absorption of photons at the p-n junction will contributeto the lateral diode sensitivity. In some embodiments, to aid theabsorption of longer length photons, the p-n junction may not beshielded with an opaque material. In the above diode embodiments,reversing the doping of the n-type and p-type contacts and/or reversingthe Schottky metals may provide a similar functioning diode with areversed electron flow.

The present invention should not be considered limited to the particularembodiments described above, but rather should be understood to coverall aspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention may be applicable, will bereadily apparent to those skilled in the art to which the presentinvention is directed upon review of the present disclosure. The claimsare intended to cover such modifications.

1. A photodiode, comprising: an n-type section; a p-type section; alaser treated semiconductor section; said laser treated semiconductorsection disposed between said n-type section and said p-type sectionsuch that said n-type section and said p-type section can generate anelectric field substantially capable of depleting at least a portion ofsaid laser treated semiconductor section of free carriers and separatingresulting electron-hole pairs generated in said laser treatedsemiconductor section.
 2. The photodiode of claim 1 wherein the lasertreated semiconductor section comprises a net doped n-type material andthe n-type section has a higher level of n-doping than the laser treatedsemiconductor section.
 3. The photodiode of claim 1 wherein the lasertreated semiconductor section comprises a net doped p-type material andthe p-type section has a higher level of p-doping than the laser treatedsemiconductor section.
 4. The photodiode of claim 1 further comprising apair of electrical contact points, one on either side of said lasertreated semiconductor section.
 5. The photodiode of claim 1 furthercomprising a substrate proximal to said laser treated semiconductorsection and comprising at least a pair of electrical contact points, oneproximal to a face of said laser treated semiconductor section and theother proximal to a face of said substrate opposing said face of saidlaser treated semiconductor section.
 6. The photodiode of claim 1further comprising a substrate proximal to said laser treatedsemiconductor section and a plurality of electrical contact pointsdisposed proximal to a face of said laser-treated semiconductor section.7. The photodiode of claim 6 wherein the n-type section partiallyencloses the p-type section and the laser treated semiconductor section.8. The photodiode of claim 6 wherein the p-type section partiallyencloses the n-type section and the laser treated semiconductor section.9. A photodiode comprising, a first Schottky contact; a second Schottkycontact; a laser treated semiconductor section; said laser treatedsemiconductor being at least partially disposed between said firstSchottky contact and said second Schottky contact; said first Schottkycontact having a higher work function than said second Schottky contact,such that said first Schottky contact and said second Schottky contactgenerate an electric field capable of substantially preventingelectron-hole pairs generated by said laser treated semiconductorsection from recombining in at least some portion of said laser treatedsemiconductor section.
 10. The photodiode of claim 9 said Schottkycontacts comprising a pair of electrical contact points, one on eitherside of said laser treated semiconductor section.
 11. The photodiode ofclaim 9 further comprising a substrate proximal to said laser treatedsemiconductor section and said Schottky contacts comprising at least apair of electrical contact points, one proximal to a face of said lasertreated semiconductor section and the other proximal to a face of saidsubstrate opposing said face of said laser treated semiconductorsection.
 12. The photodiode of claim 9 further comprising a substrateproximal to said laser treated semiconductor section and said Schottkycontacts providing a plurality of electrical contact points disposedproximal to a face of said laser-treated semiconductor section.
 13. Thephotodiode of claim 12 wherein said first Schottky contact partiallyencloses said second Schottky contact and said laser treatedsemiconductor section.
 14. The photodiode of claim 12 wherein saidsecond Schottky contact partially encloses said first Schottky contactand said laser treated semiconductor section.
 15. A photodiode,comprising: a first doped section; a second doped section; a lasertreated semiconductor section; said second doped section beingsubstantially bounded by said first doped section, said laser treatedsemiconductor section being substantially bounded by said second dopedsection.
 16. The photodiode of claim 15 further comprising, a first anda second contact; said first contact being coupled to said first dopedsection, said second contact being coupled to said second doped section.17. The photodiode of claim 16 wherein said first doped section and saidsecond doped section are substantially annular and said laser treatedsection is substantially disk shaped.
 18. The photodiode of claim 17wherein said first doped section is n doped and said second dopedsection is p doped.
 19. The photodiode of claim 17 wherein said firstdoped section is p doped and said second doped section is n doped.
 20. Aphotodiode, comprising: a first doped section comprising at least onesubsection; a second doped section comprising at least one subsection; alaser treated semiconductor section; a substrate comprising a firstside; said laser treated semiconductor section, said first doped sectionand said second doped section being disposed on said first side of saidsubstrate, said second doped section being substantially bounded by saidfirst doped section, said laser treated semiconductor section beingsubstantially bounded by said second doped section.
 21. The photodiodeof claim 20 wherein said second doped section comprises a first and asecond subsection, said second doped section first and secondsubsections being disposed on either side of said laser treatedsemiconductor section.
 22. The photodiode of claim 21 wherein said firstdoped section comprises a first and a second subsection, said firstdoped section first and second subsections being disposed on theopposite side of said second doped section first and second subsectionsfrom said laser treated semiconductor section.
 23. A photodiode,comprising a first doped section comprising at least one subsection; asecond doped section comprising at least one subsection; a laser treatedsemiconductor section; a substrate comprising a first and second side;said laser treated semiconductor section and said first doped sectionbeing disposed on said first side of said substrate, said second dopedsection being disposed on said second side of said substrate, said lasertreated semiconductor section being substantially bounded by said firstdoped section.
 24. The photodiode of claim 23 wherein said first dopedsection comprises a first and a second subsection being disposed oneither side of said laser treated semiconductor section.